1. Field of the Invention
This invention relates to a technique for performing color printing using a printing head for forming dots of a plurality of colors.
2. Description of the Related Art
Serial scan printers and drum scan printers are examples of printers that record dots while a printing head scans in the main scanning direction and the sub-scanning direction. Some of the techniques for enhancing image quality with this type of printer, and particularly an ink jet printer, include one called xe2x80x9cinterlacing,xe2x80x9d which is disclosed in U.S. Pat No. 4,198,642 and Japanese Laid-Open Patent Application S53-2040, and one called xe2x80x9coverlappingxe2x80x9d or xe2x80x9cmulti-scanning,xe2x80x9d which is disclosed in Japanese Laid-Open Patent Application H3-207665.
However, a desirable dot recording method in terms of enhancing image quality depends on the orientation of the nozzle array in the printing head. Therefore, it is preferable to apply a dot recording method that is different from conventional methods to a printer having a printing head that is different from conventional heads.
It is an object of the present invention to provide a technique for performing printing using a dot recording method that is suited to a specific printing head.
In order to solve at least some of the above problems, the present invention makes use of a printing head in which first and second dot forming element arrays are arranged in parallel in the sub-scanning direction. The first dot forming element array is constructed such that a plurality of chromatic color dot forming element groups are arrayed in a specific order in the sub-scanning direction. The second dot forming element array is constructed such that a black dot forming element group for forming black dots is formed parallel to the first dot forming element array. The black dot forming element group includes a greater number of dot forming elements than each of the chromatic color dot forming element groups does. During monochromatic printing, the recording of dots in the middle portion of a recording execution area on the printing medium is executed according to a first recording method using only the second dot forming element array, and the recording of dots in the vicinity of the rear end of the recording execution area is executed according to a second recording method in which the sub-scanning feed amount is smaller than in the first recording method. Meanwhile, during color printing, the recording of dots is executed according to a third recording method using the first and second dot forming element arrays in both the middle portion and the vicinity of the rear end of the recording execution area.
The reason for applying a recording method in which the sub-scanning feed amount is smaller in the vicinity of the rear end of the printing medium than in the middle portion of the printing medium is as follows. In general, if the number of nozzles per color actually used in printing (called the xe2x80x9cnumber of working nozzlesxe2x80x9d) is large, then there will be a tendency for the range in which effective recording cannot be executed in the vicinity of the bottom of the printing medium (the unrecordable range) to be large, and for the range in which effective recording can be executed (the effective recording range) to be small. Since the black dot forming element group includes more dot forming elements than each of the chromatic color dot forming element groups, the unrecordable area in the vicinity of the bottom of the printing medium is larger during monochromatic printing than during color printing. In view of this, during monochromatic printing a recording method is employed in which the amount of sub-scanning feed is smaller in the vicinity of the bottom of the printing medium than in the middle area, which allows the effective recording range to be expanded. On the other hand, during color printing the number of working nozzles per color is smaller than during monochromatic printing, so a satisfactory effective recording range can be maintained even if the same recording method as in the middle area is employed, and therefore the recording of dots is executed using the same recording method in both the vicinity of the rear end and the middle area of the printing medium. Thus, with the present invention, printing that is suited to color printing and monochromatic printing can be executed using a specific printing head.
When the first dot forming element array includes a yellow dot forming element group for forming yellow dots, it is preferable if the arrangement order of the plurality of chromatic color dot forming element groups in the first dot forming element array is determined such that yellow dots will be formed after other colored dots at an arbitrary position on the printing medium. It is also preferable if the plurality of chromatic color dot forming element groups include mutually equivalent numbers of dot forming elements. The above-mentioned printer may include a first sub-scanning drive mechanism that performs sub-scanning at a relatively high precision, and a second sub-scanning drive mechanism that performs sub-scanning at a relatively low precision, at least after sub-scanning feed by the first sub-scanning drive mechanism is terminated. Here, during color printing, the operation of the dot forming element arrays is controlled so that at least half of the dots formed during main scanning are accounted for by yellow dots when sub-scanning feed is executed by the second sub-scanning drive mechanism without sub-scanning feed being executed by the first sub-scanning drive mechanism in the vicinity of the rear end of the printing medium.
In the vicinity of the rear end of the printing medium, sub-scanning feed by the first sub-scanning drive mechanism is not performed, but sub-scanning feed by the second sub-scanning drive mechanism is performed, so feed precision is relatively low. However, since yellow dots stand out less than dots of other colors, if at least half of the dots are yellow, then there will be minimal loss of image quality even if the sub-scanning feed precision is low.
It is also preferable if, during color printing, black dots are formed using just the dot forming elements present at the same sub-scanning position as the dot forming elements used in a specific chromatic color dot forming element group. The specific chromatic color dot forming element group is a group with which dots can be formed on the printing medium the earliest out of the plurality of chromatic color dot forming element groups in the first dot forming element array.
In this arrangement, black dots will be formed sooner than dots of other colors at the various positions on the printing medium, which prevents the bleeding of the black dots and allows a color image of higher saturation to be obtained.
During monochromatic printing in the vicinity of the front end of the recording execution area, the recording of dots may be executed according to a fourth recording method in which the sub-scanning feed amount is smaller than in the first recording method. Also, during color printing, the recording of dots in the vicinity of the front end of the recording execution area may be executed according to the third recording method which is also used in both the middle portion and the vicinity of the rear end of the recording execution area.
In this arrangement, the effective recording range can be expanded in the vicinity of the front end of the recording execution area in monochromatic printing, while the recording of dots will be simplified in color printing.
The present invention can assume a variety of specific embodiments, such as a printer and a printing method, a computer program for realizing the function of the printer or method, a computer readable medium on which this computer program is recorded, and a data signal embodied in a carrier wave including the computer program.
The above and other objects, characteristics, examples, and advantages of the present invention should be clear from the following description of the preferred embodiments given along with the figures.